Page 75 - text book form physics kssm 2020

Chapter 2 Force and Motion I

Solving Problems Involving Impulse and Impulsive Force

Example 1
A plasticine ball of mass 0.058 kg is thrown at a velocity of 10 m s and hits the wall. It sticks
–1
to the wall. What is the impulse of the plasticine?

Solution:
Mass, m = 0.058 kg
Step 123 Final velocity, v = 0 m s
Initial velocity, u = 10 m s –1
List the given information in symbols.
–1
Step
Impulse, J = mv – mu
Identify and write down the formula used.
123
J = 0.058(0) – 0.058(10)
Step = 0 – 0.058(10)
Substitute numerical values into the 144243 = 0 – 0.58
formula and perform the calculations. = –0.58 N s (in the opposite direction to the
velocity of the plasticine)

Example 2

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A golfer hits a golf ball of mass 45.93 g at a velocity of 50 m s . If the impact time is 0.005 s,
what is the impulsive force acting on the golf ball?
Solution:

–1
–1
m = 0.04593 kg, u = 0 m s , v = 50 m s , t = 0.005 s
mv – mu
Impulsive force, F =
t
0.04593(50) – 0.04593(0)
=
0.005
= 459.3 N (acting in the same direction as the velocity of the golf ball)

Formative Practice 2.7
2.7
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1. In a car collision test, a car of mass 1 500 kg hits the wall with a speed of 15 m s . The car
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bounces back with a speed of 2.6 m s . If the collision time is 0.15 s, calculate the:
(i) impulse in the collision
(ii) impulsive force acting on the car
2. A football player kicks a ball of mass 450 g with a force of 1 500 N. Th e contact time of his
shoe with the ball is 0.008 s. What is the impulse on the ball? If contact time is increased to
0.013 s, what is the velocity of the ball?

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2.7.2
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